Summary

Although there is considerable evidence that depolarization of nerve cell terminals leads to the entry of Ca2+ and to the secretion of neurohormones and neurotransmitters, the details of how ionic currents control the release of neuroactive substances from nerve terminals are unknown. The small size of most nerve terminals has precluded direct analysis of membrane ionic currents and their influence on secretion. We now report that it is possible, using patch-clamp techniques, to study stimulus--secretion coupling in isolated peptidergic nerve terminals. Sinus gland terminals from Cardisoma are easily isolated following collagenase treatment and appear morphologically and electrically very similar to non-dissociated nerve endings. We have observed two types of single-channel currents not previously described. The first (‘f’) channel is activated by intracellular Na+ and the second (‘s’) by intracellular Ca2+. Both show little selectivity between Na+ and K+. In symmetrical K+, these cation channels have mean conductances of 69 and 213 pS, respectively. Furthermore, at least three types of Ca2+ channels can be reconstituted from nerve terminal membranes prepared from sinus glands. Nerve terminals can also be isolated from the rat neural lobe. These neurosecretosomes release oxytocin and vasopressin, in response to membrane depolarization, only in the presence of external Ca2+. The depolarization of the nerve endings is associated with an increase in intracellular free Ca2+ concentration and this increase, measured using a fluorescent indicator, is abolished by Ca2+ channel blockers. Channels similar in their properties to the f and s channels also exist in rat neural lobe endings. Since these channels have not been found in other neurones or neuronal structures they may be unique to peptidergic nerve terminals.

Similar articles

Other journals from The Company of Biologists

Editor-in-Chief Hans Hoppeler and Monitoring Editor Craig Franklin highlight new initiatives at JEB in response to the COVID-19 pandemic. To continue advancing knowledge in the field, we are encouraging proposals for meta-analysis papers and timely Reviews and Commentaries within the JEB remit. New grant categories analogous to the Travelling Fellowships will fund collaborative data projects and the development of online resources for early-career researchers. Read their Editorial to find out more.

In their Review, Hanane Hadj-Moussa and Ken Storey assess OxymiRs in over 20 animal species. They reveal a lack of universal microRNA strategy, showing that instead there are species-specific responses to oxygen deprivation.

Researchers at nine institutions in Ireland can now publish an unlimited number of Open Access articles in JEB, immediately and at no cost to them, following a three-year Read & Publish agreement between The Company of Biologists and IReL. Find out more and see the growing list of participating institutions.

We are expanding the Conversation series to focus on the experiences of researchers out in the field. We’ll go behind the scenes as researchers tell us about their experiences on trawlers, in deserts, up mountains and in the remotest regions of the poles. Find out more about the series in the Editorial.

In the first interview, JEB author and editor Craig Franklin talks about the risks and challenges of working in remote areas with animals in their natural environment.